Hi all,

this changeset adds a new property to PluggableWidgetSpecs, #available. It can be used to show tool contents dynamically based on the result of a message send. Consider this toolbuilder method:

    ^ aBuilder pluggablePanelSpec new
        layout: #vertical;
        children: (OrderedCollection new
            add: (aBuilder pluggableTextSpec new
                model: self;
                getText: #input;
                setText: #input:;
                yourself);
            add: (aBuilder pluggableTextSpec new
                model: self;
                available: #outputAvailable;
                getText: #output;
                yourself);
            yourself)
        yourself

Demo: ["available.gif"]
Another helpful example could be dynamic displaying of a single button in a panel without needing to rebuild the entire panel (which is overhead and might remove relevant state).

Changeset summary:
- PluggableWidgetSpec >> #available[:] accessors
- getAvailableSelector accessors and relevant #update: logic for almost all Morphic tool-buildable widget classes such as PluggableButtonMorphPlus, PluggableListMorphPlus, etc.
- Patch in MorphicToolBuilder to set getAvailableSelector
- Morph >> #makeAvailable:: Shows/hides and enables/disables the layout of a morph at the same time. I often use this together; see [1] for further information.
- DemoTool that you can see above for quick demonstration. In any case I think a very simple example for the toolbuilding method would not harm in the MorphicExtras-Demos category.

I request to review and merge or discuss this proposal. :-)

Note: I do *not* ask to hide many buttons in our default Trunk tools, which would be a major UX change which for sure would have many disadvantages. But I see some advantages in providing this behavior for other tools which follow different UX guidelines.

Best,
Christoph

[1] https://forum.world.st/Morphic-equivalent-of-display-none-tp5114410p5114419.html

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